1. Field of the Invention
The present invention relates to a method of manufacturing carbon cylindrical structures as represented by carbon nanotubes and, more particularly, to a method of manufacturing carbon cylindrical structures using a clean technology that is applicable to semiconductor electronics.
The present invention also relates to a method of efficiently manufacturing carbon nanotubes with controlled diameter and/or number of walls, and to single wall or multi-wall carbon nanotubes which are obtained by such a manufacturing method and which have uniform diameter and/or number of walls and thereby have uniform electrical properties.
The present invention further relates to a biopolymer detection device, and a biopolymer detection method, carbon nanotube structures used for same, and a disease diagnostic apparatus, which is capable of easily and reliably detecting a target biopolymer contained in a sample and which thereby permits diagnosis of a disease to be carried out efficiently.
2. Description of the Related Art
As a new carbon material, carbon nanotubes have attracted wide attention because of their unique physical properties. A carbon nanotube has a cylindrical structure of rolled-up graphite sheet in which hexagonal-shaped (six-membered ring) units of carbon atoms are bound to each other by sp2+ bond, very strong bond between carbon atoms. Carbon nanotubes are nano-structures formed by carbon atoms in a self-organizing fashion, with the minimum diameter of 0.4 nm, and the length ranging as long as several hundreds μm, and are characterized by extremely small dimensional fluctuation. Electrical conductivity of a carbon nanotube varies widely from that of a semiconductor to that of a metal depending upon the chirality (the manner in which the graphite sheet is rolled up). In nanotubes exhibiting electrical conductivity of a metal, conduction by non-scattered charge carriers (ballistic conduction) is seen. In this case, the resistance value becomes independent of length, and the so-called quantum resistance (6.5 kΩ) is observed.
Possible application to various fields is envisaged for carbon nanotubes having such numerous characteristics. As an example, application to semiconductor electronics are being considered.
Several methods for manufacturing carbon nanotubes are known such as, for example, an arc discharge method, a laser ablation method, a thermal CVD method, a plasma enhanced CVD method, etc. In above-mentioned arc discharge method and laser ablation method, obtained carbon nanotubes include single wall carbon nanotubes (SWNT: Single Wall Nano Tube) that consists of a single graphite sheet, and multi-wall carbon nanotubes (MWNT: Multi Wall Nano Tube) that consists of a plurality of graphite sheets.
In thermal CVD methods and plasma enhanced CVD methods, MWNTs are produced predominantly. The above-mentioned SWNT has the structure in which a single graphen sheet of hexagonally linked carbon atoms bound via a strong bond called sp2+ bond between carbon atoms is rolled up in the form of a tube. The carbon nanotube thus formed may have a diameter of 0.4 nm and length as long as several hundreds μm.
Regardless of the methods employed for manufacturing carbon nanotubes, control of chirality, control of diameter and control of length of the carbon nanotubes are problems remaining to be solved. Especially if these materials are to be applied to the field of semiconductor electronics, these problems have to be solved by using a clean technology.
Methods using arc discharge or laser ablation are not suited to mass production or to the manufacture of integrated circuits. In contrast, it can be said that methods using CVD for manufacturing carbon nanotubes may be applicable to semiconductor electronic device such as integrated circuits.
In CVD methods, a catalyst metal is considered to be necessary for growing carbon nanotubes. It has been reported that the diameter of the grown carbon nanotubes may be controlled by using the catalyst metal in the form of micro-particles and varying the size of the micro-particles. However, it has been found very difficult to fabricate the micro-particles of a catalyst metal with diameter controlled in the range of nanometers in accordance with the diameter of the carbon nanotubes. Thus, an alternative method is currently employed in which a catalyst metal film is formed on the growth substrate by sputtering or the like, and the surface of the metal film is bombarded with a high speed ion beam to produce a rugged structure of nanometer size on the surface, and the produced rugged structure is used in place of micro-particles of the catalyst metal. It can be easily surmised that it is difficult to form the rugged structure uniformly on the surface of the metal film so as to replace the micro-particles of the catalyst metal, especially when the diameter is small.
Another method is also attempted in which micro-particles are directly deposited on the surface of the substrate. In this method, coalescence of micro-particles takes place by collision of micro-particles with each other before they reach the substrate surface, or by diffusion of micro-particles on the substrate surface, and tends to produce secondary particles with larger diameters, so that it is difficult to produce smaller micro-particles.
In CVD methods, on the other hand, growth temperature of about 600 to 700° C. is usually employed. If a substrate having micro-particles of catalyst metal deposited thereon is heated to such a high temperature, the micro-particles may move, by rotation or the like, while the carbon nanotubes are growing so that it may twist the growing nanotubes or otherwise affect the chirality. Therefore, it is highly probable that the nanotubes having desired characteristics are extremely difficult to obtain.
On the other hand, the above-mentioned carbon nanotubes are nano-structures in which carbon atoms grow in self-organizing fashion, and as such, are characterized by extremely small dimensional fluctuation. It is also known that the electrical conductivity of the carbon nanotubes varies widely depending upon the difference of the manner of rolling-up of the tube (chirality) from that of a semiconductor to that of a metal. It is also known that, in the case of carbon nanotubes having the electrical conductivity of a metal, if there is no lattice defect, conduction of non-scattered charge carriers (ballistic conduction) is seen, and resistance value is the quantum resistance (6.5 kΩ) that is independent of length.
However, SWNTs grown in arc discharge method or laser ablation method are in the form of soot and contain a large amount of impurities so that refining to high purity is difficult and selective growth on a patterned substrate is impossible. On the other hand, selective growth on a patterned substrate is possible in a thermal CVD method or a plasma enhanced CVD method, and transition metals (for example, Ni, Co, Fe, etc.) are used in the form of a vapor deposition film, a sputtered film or ultra-fine particles as catalyst metals for carbon nanotubes.
When carbon nanotubes are grown on such a catalyst metal by a thermal CVD method or a plasma enhanced CVD method, the diameter of the grown nanotube is influenced by the grain boundaries, film thickness, or the like, of the thin film of the catalyst metal. Therefore, the diameter of the carbon nanotubes has been controlled by annealing of the catalyst metal to obtain finer particles. However, this method for obtaining finer particles of a catalyst metal has a drawback that the diameter of the catalyst metal cannot be made smaller than about several nm.
The Human Genome Project is a world-wide project in which various countries in the world have participated to analyze and determine the sequence of human genome (human DNA). It was started in 1990s, and in summer in the year 2000, a draft version was published containing complete sequencing information of human genome (DNA). If any part of this human genome (DNA) is correlated with some biological function of human body, it would bring about a new development in technology related to life science including disease diagnostics, disease therapy, etc.
For example, in conventional diagnosis of diabetes, only a broad classification into type I and type II diabetes has been done based on the insulin production capability of the patient's body. In the case of above-mentioned diabetes, the disease occurs as a result of inadequate regulation of blood sugar due to an imbalance of the function and amount of a plurality of proteins interacting with each other in complicated way, such as receptors of blood sugar and enzymes that synthesize or decompose insulin in accordance with the value of blood sugar. In conventional diagnosis of diabetes, however, there is a problem that the direct cause of the diabetes cannot be known. But, the sequencing information of human genome (DNA) obtained by the Human Genome Project offers us the complete information about the genes (DNA) encoding amino acid sequence of various proteins such as the receptors and enzymes involved in the regulation of the blood sugar value. Thus, by analyzing the gene (DNA) information, we can know the protein directly responsible to the anomalous regulation of the blood sugar value, so that, instead of the broad classification of the diabetes into diabetes of type I and type II, diabetes can be classified more specifically into subtypes, and more suitable diagnosis and therapy of the diabetes would become thereby possible. It is expected that, in the near future, diagnosis and therapy of a disease can be carried out in more suitable manner by analyzing the function and amount of a plurality of proteins in close functional relation with each other.
At present, no established method capable of quickly determining the amount of a plurality of proteins in close functional relation with each other, as described above, is known except for the method that combines two dimensional electrophoresis with mass spectroscopy. However, even with this method, there are problems that effective information for diagnosis and therapy of a disease cannot be obtained sufficiently and measurement cannot be carried out quickly.
On the other hand, as regards DNA, a DNA chip has been provided that is capable of quickly quantifying the amount of DNA in a sample. This is done by introducing in advance a fluorescent labeling dye during the amplification (increase of amount) by PCR (polymerase chain reaction) of the DNA to be measured, and by measuring the fluorescent light intensity based on the DNA in the sample bound to the complementary DNA arranged in an array. However, as for proteins, there is no amplification method for proteins corresponding to the PCR method for DNA, and in addition, reactivity with a fluorescent labeling dye is different for different proteins so that it is difficult to introduce a fluorescent labeling dye uniformly to various proteins. For these reasons, a chip capable of quantifying the amount of proteins in a sample has not been provided until now. Therefore, it is desired to develop an array chip and associated technology capable of quickly quantifying the amount of a specific protein without using a fluorescent labeling dye.